package Text;

import java.util.Scanner;

public class Text4 {
    static int shu(int a){
        if(a==1||a==2){
            return 1;
        }
        return shu(a-1)+shu(a-2);
    }
    public static void main(String[] args) {
        //求斐波那契数列的第n项。(迭代实现)
        Scanner sc=new Scanner(System.in);
        int a=sc.nextInt();

        System.out.println(shu(a));
    }
}
